This invention is related to a method for the automatic cropping of images, and is particularly suitable to images that are texture-free, or relatively texture-free.
A typical image contains some regions where intensity level, and color, are uniform, and other regions where intensity level and color vary considerably. For instance, the "background" of an image may be uniform with a distinct "edge" separating the background from the "foreground." For example, a portrait typically comprises a subject set against a uniform backdrop or background, such that a sharp edge or boundary exists between the subject and the background.
Frequently, it is desirable to select only a particular region of an image, and to reproduce the selected region, thereby eliminating unwanted or excess background to give the image a more desirable composition. This selection process is referred to as cropping. Often, images are cropped to the foreground and most of the background is discarded.
Cropping is usually done by hand or requires operator interaction in order to properly select the subject and cropping dimensions. For example, U.S. Pat. No. 4,809,064 to Amos et al. discloses an apparatus for printing a selected portion of a photographic negative onto a photosensitive paper to form an enlarged and cropped photographic print. However, the apparatus requires human operation to determine the crop. Similarly, U.S. Pat. No. 5,115,271 to Hagopian discloses a variable photographic cropping device for maintaining multiple constant proportions of a visible area that includes a pair of masks situated in a housing having a central window. The apparatus also requires an operator.
In the field of automatic image enhancement, methods are known for improving the contrast in a natural scene image or altering the sharpness in a reproduction of an electronically encoded natural scene images. Such methods have been disclosed, for example, in U.S. Pat. Nos. 5,450,502 and 5,363,209 to Eschbach et al., the disclosures of which are incorporated herein by reference. However, such automatic image enhancement methods do not disclose automatic image cropping.
For high quality publication and printing, manual cropping may be preferred for artistic reasons. For large volume printing, including, but not limited to, passport photographs, yearbooks, catalogs, event books, portraits, other images with uniform backgrounds, and the like, it is desirable to have the option to use autocropping to enhance productivity and uniformity of the cropping process.